Asynchronous Operating Ability of Turbo Generator With Different Field Discharge Resistors

Asynchronous operation of a turbo generator after the loss of field caused by the excitation fault can avoid large-scale blackout and, therefore, improve the reliability of the power systems. In order to consume the magnetic energy stored in the field winding as soon as possible, a field discharge resistor (FDR) is often connected to the field winding after the excitation fault, but it may affect the asynchronous operating ability of the turbo generator and result in the overvoltage of the field winding. In order to study the influence of the FDR on the asynchronous operating ability of turbo generator, a field-circuit coupled time-stepping finite-element model is established, and the experimental validation is performed on a model machine. For a 300-MW turbo generator, the electromagnetic characteristics, such as torque pulsation, air-gap radial flux density, and flux density distribution, are calculated and compared under different FDRs. The variation of the asynchronous operating ability along with the increase of the value of the FDR is revealed. Under the consideration of the withstanding voltage of field winding, the suitable value of the FDR that can improve the asynchronous operating ability is obtained. The results could provide a theoretical basis for improving the asynchronous operating ability of the turbo generator.